The Museum of HP Calculators

HP Forum Archive 20

[ Return to Index | Top of Index ]

Maintenance and Durability: From NIB to abused calculators
Message #1 Posted by Fabricio on 19 Feb 2012, 10:26 a.m.

Im following this thread from HERE

Quote:
... Even an unused one cannot be guaranteed to survive for long because all electronic components have their respective lifetimes even without much use.

So the issue is, how to protect and keep a calculator for the next 20 to 30 years from 2012 on? My question is mainly headed to the vintage pioneer (27s, 32sii, 42s), clamshell (28s) and Charlemagne series (48s, 48GX).

I have my *stock* that is not in use packed without batteries, and am planning to unpacked them every 4-months or so to use them for a day or two just to keep their internals on action from time to time. Aside from the basics (not dropping the unit, putting the case for preventing it from unnecesary dust), what else would you recomend for both units in daily use and units in storage?

Thanks in advance!

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #2 Posted by David Ramsey on 19 Feb 2012, 11:08 a.m.,
in response to message #1 by Fabricio

Other than storing them in a non-oxygen atmosphere, I think you're doing about all you can. Storing them without batteries is the biggie, of course. As far as I know the only electronic components that will fail under these circumstances are electrolytic capacitors, and I think that occasional power-on time helps retard this.

            
Re: Maintenance and Durability: From NIB to abused calculators
Message #3 Posted by From Hong Kong on 19 Feb 2012, 11:44 a.m.,
in response to message #2 by David Ramsey

Quote:
Other than storing them in a non-oxygen atmosphere, I think you're doing about all you can. Storing them without batteries is the biggie, of course. As far as I know the only electronic components that will fail under these circumstances are electrolytic capacitors, and I think that occasional power-on time helps retard this.

My Sharp PC-E500S was bought new around 1999. I removed the 4 AAA batteries but kept the button cell for memory backup in the battery compartment. A 32KB RAM card with a backup battery was installed in the machine. I remember that it was turned on one to two years ago. One day I put new batteries into the machine but I couldn't turn it on. I replaced all button cells in the machine and in the RAM card with new ones but it could't still be turned on. After several days, I could suddenly turn it on! I'm not sure whether there were problems in certain electrolytic capacitors.

Edited: 19 Feb 2012, 11:45 a.m.

            
Re: Maintenance and Durability: From NIB to abused calculators
Message #4 Posted by Cristian Arezzini on 19 Feb 2012, 11:49 a.m.,
in response to message #2 by David Ramsey

Quote:
As far as I know the only electronic components that will fail under these circumstances are electrolytic capacitors,

I have two counter-examples for this. I have two calculators: a Ti-68 and an Elorg-51. Both stored for years in a box without batteries, and with silica-gel to keep humidity low. The Ti-68 developed a fault at the flex cable connecting the display to the motherboard. Even though it doesn't move or actually flex in the Ti68, still it got degraded somehow, leading to display problems (in my case, no decimal point was displayed).

On the Elorg 51, I don't know how it happened, but the LCD became "slow" - i.e. the contrast is good, it doesn't look "dim", but it takes maybe 2-3 seconds to "change aspect". If I press a few numbers fast, you can actually see them slowly appearing, right to left. It's not a CPU-slow-speed thing because calculations happen fast enough.

Cristian

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #5 Posted by Thomas Chrapkiewicz on 19 Feb 2012, 11:28 a.m.,
in response to message #1 by Fabricio

This is not necessarily a recommendation for prevention, but awareness.

The 48 series (and others?) relay on a spongy/conductive- 'zebra strip' for the display connections. This sponge loses its resilience with time, resulting in loss of connection(s).

Also, in the 48, the connections between the keyboard flexboard and the main pc board are simply 'connected' by pressure from behind with a piece of sponge. This type of 'connection' is fundamentally headed for failure from loss of resilience and the inevitable oxidation on the contacts. This has already been witnessed for years.

I've disassembled 48s, 48g and 38g families. If anyone could use pictures, or would like more details, drop me an email.

TomC

            
Re: Maintenance and Durability: From NIB to abused calculators
Message #6 Posted by Bart (UK) on 19 Feb 2012, 1:12 p.m.,
in response to message #5 by Thomas Chrapkiewicz

This sponge that presses the keyboard connector to the PCB seems to becoming a more prevelent failure. An easy fix really, but unfotunately the Pioneers and 48-series are the most difficult to take apart.

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #7 Posted by aj04062 on 19 Feb 2012, 12:45 p.m.,
in response to message #1 by Fabricio

I wonder if there is some MIL Spec grade storage bags that might help. I package items I sell in these types of bags. They inhibit corrosion and moisture. Problem is, I don't think either of these are the culprits to lost elasticity in pressure contacts.

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #8 Posted by John B. Smitherman on 19 Feb 2012, 1:01 p.m.,
in response to message #1 by Fabricio

A dry and oxygen free environment is probably the best you can do. Maybe using nitrogen and desiccant would help. Or, think like an ancient Egyptians and use the power of the pyramid. ;-)

Good luck with your preservation!

John

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #9 Posted by Bart (UK) on 19 Feb 2012, 1:06 p.m.,
in response to message #1 by Fabricio

Avoid temperature extremes. I lost the screen on a PC-1251 when it was left in an unheated room during a very cold night last winter (we were away visiting family for a few days).

Electrolytic caps (and some tantalums) are another weak point. This is because the dielectric layer is formed from the electrolyte in the cap and breaks down if the cap is left discharged for long periods of time (years). Powering on every 4 months should be fine. However, if you do come accross one that has been left unpowered for a very long time, do not just power it up as the current through the cap can permanently damage it. Connect a 1k ohm resistor in series with the normal supply voltage for 24 hours for the capacitor to re-form. In old calculators I replace the electrolytic caps as standard (particularly prevalent in those with VFD and Panaplex displays).

Be careful with the use of cleaning agents, because although they may be keyboard friendly, if it gets to rubber strips these can deteriorate quicker and fluids can also damage the connection of heat seal connectors (more commonly used to connect LCDs in modern calculators).

As for failures of other electronic components, these are pretty random - just depends on your luck (except for design flaws, e.g. the woodstock charging circuit).

            
Re: Maintenance and Durability: From NIB to abused calculators
Message #10 Posted by Garth Wilson on 20 Feb 2012, 3:27 a.m.,
in response to message #9 by Bart (UK)

Quote:
Avoid temperature extremes. I lost the screen on a PC-1251 when it was left in an unheated room during a very cold night last winter (we were away visiting family for a few days).
Hmmm... I wonder if it could have been from something else. I had an LCD down to -55 deg C 10+ years ago in a test for a product in development, and it did not hurt it. It wouldn't work down there, but it was fine when brought back up to -20 or higher again. This was admittedly a wide-temperature-range one which was supposed to be able to go down to -40, but I expect the commercial grade should be able to go past freezing with no problem.

Edited: 20 Feb 2012, 3:28 a.m.

                  
Re: Maintenance and Durability: From NIB to abused calculators
Message #11 Posted by Bart (UK) on 20 Feb 2012, 5:21 a.m.,
in response to message #10 by Garth Wilson

I agree that one would expect it to withstand temperatures to -10 deg C, many commercial parts are rated down to this (I estimate that the room may have briefly been as low as -5). I have a dozen other LCD calculators in the same room, they are all OK. I opened the 1251 up to see if the screen was under any stress, but it all seemed fine. It may have been a weak part, but I have seen quite a few 1251's with leaky screens, so perhaps the LCD quality for that particular model is not too good. As I don't know if any of my other calculators happen to have a 'boderline' part, I now try to keep them within +10 to +25 degrees C range.

Edit:
Just to describe what happened, I was writing a program on it before we went away, (leaving it the cold upsstairs room) and on return I fetched and I noticed the dark spot in the upper left corner. I let it warm up for a day in the lounge. The spot then mostly dissapeared, but a slight discouleration remained. I then opened it up to see if the screen was under any stress, but it all seemed fine. However, over the following months that corner went dark again and it spread - and took on the typical "LCD bleeding" look.

Edited: 20 Feb 2012, 5:36 a.m.

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #12 Posted by Bruce Larrabee on 19 Feb 2012, 11:27 p.m.,
in response to message #1 by Fabricio

What was said about the 48s applies to all the clam shell models I think. That can be repaired. If you are good at welding plastic.

I would think that if you are going to store them a very long time pulling the caps out might be a good idea.

And then the nitrogen.

      
permanent storage is hardly possible
Message #13 Posted by Frank Boehm (Germany) on 20 Feb 2012, 5:07 a.m.,
in response to message #1 by Fabricio

- failure of electrolytic capacitors, these can be replaced
- disintegration of anything made out of plastics, including foam (used for key feedback, instead of springs) and casing parts (screw posts cracking away)
- corrosion of contacts, including key contacts, zebra strip contacts, display contacts
- corrosion of the LCD

For optimum storage, I'd recomment a dark, zero moisture, 10oC cold storage. One thing to remember: soft cases should not come into contact with the calculator, best is to keep them seperately (they often contain softeners, which will damage plastic parts).

            
Re: permanent storage is hardly possible
Message #14 Posted by From Hong Kong on 20 Feb 2012, 10:57 a.m.,
in response to message #13 by Frank Boehm (Germany)

Quote:
For optimum storage, I'd recomment a dark, zero moisture, 10oC cold storage. One thing to remember: soft cases should not come into contact with the calculator, best is to keep them seperately (they often contain softeners, which will damage plastic parts).

I've a Sharp PC-1250A put inside its soft case. One day I discovered that some 'oil' coming out from the inner sides of the soft case. The front and rear sides of the computer were in contact with the inner sides. The front side including the display is ok so far. However, the rear side is coated with some slightly sticky thing. I've no idea about this coating. Maybe something with softners.

The same problem causes a coating on the display of my Casio FX-603P. I've to rub the display by my thumb regularly to remove the coating.

      
Re: Maintenance and Durability: From NIB to abused calculators
Message #15 Posted by Fabricio on 21 Feb 2012, 11:36 a.m.,
in response to message #1 by Fabricio

Thanks to all for your suggestions!


[ Return to Index | Top of Index ]

Go back to the main exhibit hall